Field device for determining and monitoring process variable in process automation systems

ABSTRACT

A field device for determining or monitoring a process variable in process automation. The field device includes: a sensor, which works according to a defined measuring principle; and a control/evaluation unit, which conditions and evaluates the measurement data delivered by the sensor; wherein the control/evaluation unit is embodied at least partially as a reconfigurable logic chip FPGA having a plurality of dynamically reconfigurable function modules; wherein an interface is provided, via which the control/evaluation unit receives sensor- and application-specific information concerning a defined sensor type in a defined process application; and wherein the control/evaluation unit so configures the function modules corresponding to the sensor- and application-specific information, that the field device is optimally adapted to the process variable to be ascertained, or to be monitored, and to the current process application of the field device.

The invention relates to a field device for determining or monitoring a process variable in process automation. The field device includes: A sensor, which works according to a defined measuring principle; and a control/evaluation unit, which conditions and evaluates the measurement data delivered by the sensor.

In automation technology, especially in process automation technology, field devices are often applied, which serve for determining and monitoring process variables. Examples of such field devices include fill level measuring devices, flow measuring devices, analytical measuring devices, pressure and temperature measuring devices, moisture and conductivity measuring devices, and density and viscosity measuring devices. The sensors of these field devices register the corresponding process variables, e.g. fill level, flow, pH value, substance concentration, pressure, temperature, moisture, conductivity, density or viscosity.

Subsumed under the term ‘field devices’ are, however, also actuators, e.g. valves or pumps, via which, for example, the flow of a liquid in a pipeline or the fill level in a container is changeable. A large number of such field devices are available from members of the firm, Endress +Hauser.

As a rule, field devices in modern automation technology plants are connected via communication networks (HART multidrop, point to point connection, Profibus, Foundation Fieldbus, etc.) with a superordinated unit, which is referred to as a control system or control room. This superordinated unit serves for process control, process visualizing, process monitoring, as well as for start-up, or for servicing, of the field devices.

Necessary supplemental components for operation of fieldbus systems, i.e. components, which are directly connected to a fieldbus and which serve especially for communication with the superordinated units, are likewise frequently referred to as field devices. These supplemental components include e.g. remote I/Os, gateways, linking devices or controllers.

Known also is to integrate fieldbus systems in enterprise networks, which work on an Ethernet basis. These enterprise internal, bus systems permit access to process, or field device, information from different areas of an enterprise. Moreover, it is state of the art to connect company networks with public networks, e.g. the Internet, for the purpose of worldwide communication.

For servicing and for start-up of field devices, corresponding operating programs are necessary. Known, in such case, are, for example, the operating program FieldCare of Endress+Hauser, the operating program AMS of Emerson and the operating program Simatic PDM of Siemens.

Serving for control and monitoring of plants having a plurality of field devices are control system applications, such as e.g. Simatic S7 of Siemens, Freelance of ABB and Delta V of Emerson.

An essential aspect of open communication systems, such as e.g. Profibus, Foundation Fieldbus or HART, is the interoperability and exchangeability of devices of different manufacturers. Thus, sensors or actuators of various manufacturers can be applied without problem together in a plant. Also an option is to replace a field device of one manufacturer with a functionally equal field device of another manufacturer, whereby the customer has a highest measure of freedom in the configuration of its process installation.

Field devices are becoming increasingly complex as regards their functionality. Besides pure, measured value processing, diagnostic tasks and, above all, communication tasks, which the field devices must fulfill with respect to the installed bus systems, are becoming always more complex. Still more complex are functionalities in field devices having multisensor capability. These field devices must be able to determine or to monitor, simultaneously, at least two process variables. In order to meet these increasing requirements, a number of microcontrollers are often provided in parallel in a field device.

An advantage in the use of microcontrollers is that, via application-specific software programs, which run in these microcontrollers, the most varied of functionalities are implementable. In addition, program changes can be made relatively simply. Program controlled field devices are flexible to a high degree. This high flexibility is, however, gained with the disadvantage, that, because of the sequential progression through the program, the processing speed is slowed.

In order to increase processing speed, when it makes sense, ASICs—Application Specific Integrated Circuits—are applied in the field devices. Through their application-specific configuration, these chips can process data and signals significantly faster than a software program can. ASICs are excellent especially for computationally intensive applications.

Disadvantageous in the case of the application of ASICs is that the functionality of these chips is fixedly predetermined. A subsequent changing of the functionality of these chips is not directly possible. Furthermore, the use of ASICs makes sense only in the case of relatively large piece numbers, since the developmental effort and the therewith connected costs are high.

In order to avoid the drawback of fixedly predetermined functionality, WO 03/098154 proposes a configurable field device, wherein a reconfigurable logic chip in the form of a FPGA is provided. In the case of this known solution, the logic chip has at least one microcontroller, which is also referred to as an embedded controller. The logic chip is configured during system start. After the configuration is finished, the required software is loaded into the microcontroller.

The reconfigurable logic chip required in such case must have available sufficient resources, such as sufficient logic, wiring and memory resources, in order to fulfill the desired functionalities. Logic chips with many resources require much energy, and, with that energy, their use in process automation limitless. Disadvantageous in the use of logic chips with few resources, and, thus, having smaller energy consumption, is the considerable limitation in the functionality of the corresponding field device.

An object of the invention is to provide a field device, which is suitable for flexible use in the most varied of applications in process automation technology.

The object is achieved by features including that the control/evaluation unit is embodied, at least partially, as a reconfigurable logic chip FPGA having a plurality of dynamically reconfigurable function modules—involved is, thus, a partially dynamically reconfigurable logic chip. Furthermore, an interface is provided, via which the control/evaluation unit receives sensor- and application-specific information concerning the defined sensor type in the defined process application. The control/evaluation unit configures the function modules corresponding to the sensor- and application-specific information in such a manner, that the field device is adapted optimally to the process variable to be ascertained, or to be monitored, and to the current process application. The selected sensor- and application-specific information is, for example, loaded during manufacture into the flash memory and subsequently configured by the control/evaluation unit. Alternatively, also the complete functionality for the most varied of applications and sensors can be loaded into the flash memory, so that, subsequently, as regards selection of the sensor for the particular application, a large flexibility is present. An option is, then, to reconfigure the field device for another application at a later point in time, to the extent desired.

Preferably, the function modules involve microprocessors with different bus widths, A/D converters or D/A converters with different bit resolutions, signal filters with different filter functions, different scalings of evaluating algorithms (or polynomials, as the case may be), different modems, different electrical current control units or operating units for different in/output units.

An advantageous embodiment of the field device of the invention provides, that the control/evaluation unit has at least one static region, in which is permanently configured at least one fundamental component, such as, for example, the microcontroller. Since the components in the static region are preferably permanently connected, they are distinguished by a high processing speed. A partially dynamic reconfiguration makes, here, little sense, since—in the case of application of only one microcontroller—this must be configured permanently in its function as control unit for the configuring of the function modules.

Moreover, it is provided in connection with the field device of the invention, that the sensor-specific information involves information, which characterizes the sensor in its function for determining or monitoring a process variable via a defined measuring principle. If, for example, the process variable to be monitored is flow, then flow measuring devices can be applied, which operate, for example, based on the Coriolis principle or on the principle of Karman's vortex street. Furthermore, flow can be ascertained via measuring the travel-time difference of ultrasonic measurement signals, or by the principle of electromagnetic induction.

Of course, the process variable can be the most varied of physical or chemical, process variables. By way of example, reference is made here to the following process variables: Fill level, pressure, flow, temperature, conductivity, pH-value, turbidity, density, viscosity or concentration of a chemical substance.

The application-specific information can include information concerning the defined application, in which the field device is applied in the process. Thus, this information can be information concerning in which operational manner e.g. a pressure sensor works. Possible types of operation of a pressure sensor include pressure measurement, fill level measurement and flow measurement. In the case of pressure measurement, it is, in turn, distinguished, whether the field device measures relative pressure, absolute pressure or pressure difference, compensated with relative pressure.

Furthermore, the application-specific information can be information on whether the field device is applied in a process, wherein the process variable to be measured essentially changes continuously, or whether, in the monitored process, abrupt changes of the process variable are to be expected.

An example of an-abruptly changing process variable is a pressure shock, or so-called water hammer. A pressure shock arises, when, in a liquid conveying pipeline, a retractable assembly, or a valve, is closed, or opened, too rapidly. The kinetic energy of the liquid column moving in the pipeline brings about, in front of the retractable assembly, through its low compression module, a very rapid rise in pressure. The same happens behind the retractable assembly. However, there arises there first a vapor bubble having a lower pressure, while the liquid column moves further. At a given instant, however, because of the, pressure drop reigning in the pipeline, the liquid column reverses its direction of movement and pounds back into the retractable assembly. Depending on the intensity of the impact, the retractable assembly and/or the connecting pipelines can be destroyed. Similar problems can occur during the opening of the retractable assembly. It is quite usual, that pressure changes before and behind the retractable assembly can lie in a range of 20 bar to 100 mbar absolute. These abrupt pressure increases and pressure decreases occur so rapidly, that they are not at all measurable with conventional pressure measuring devices. Conventional pressure measuring devices are distinguished, preferably, by a high accuracy of measurement in the case of slowly changing pressures. Since the extreme pressure fluctuations lead, not seldomly, to the failure of the pressure measuring device, it is indispensible in the context of predictive maintenance to register pressure surges, to log them, and, on occasion, suitably to react to them.

With the field device of the invention, whose control/evaluation unit is configured to serve as that of a pressure measuring device, the occurrence of water hammers can be detected. If is the occurrence of water hammer and its effects are detectable, then suitable countermeasures can be taken, to counteract abrupt rising and falling of pressure values in the pipeline. For example, the pipeline can have rapidly controllable valves, which, in the presence of knowledge of the pressure shock, perform suitable compensation procedures.

In order to detect abrupt changes and subsequently to be able to react appropriately, a further development of the field device of the invention provides that, in ongoing measurement operation, a monitoring function checks, whether abrupt changes of the process variable are occurring. If abrupt changes are evident, or their occurrence is known in advance, then the control/evaluation unit configures function modules, especially the A/D, and D/A, converters and filter to have higher bit-resolution than is the case, when the process variable slowly changes or when it essentially assumes a constant value. In the case of established pressure measuring devices, the main emphasis is on providing a pressure measurement having a high accuracy of measurement. The electronic evaluation components are so selected, that they have a high bit resolution. The processing speed is, thus, relatively slow. In order to detect the pulse-like water hammers, in contrast, a high processing speed is required, which is only doable, when converter components having a smaller bit resolution are applied. According to the invention, those function modules are always configured, which are optimally matched to the conditions reigning in the process.

According to the invention, it is, in an alternative embodiment, also an option, always, when a retractable assembly is actuated, to configure function modules, which are able to detect abrupt pressure changes, while, in normal measurement operation, the function modules are so configured, that they are designed for a high accuracy of measurement. The corresponding information is received by the control/evaluation unit via a suitable monitoring function, which is made available to it, for example, via the bus.

Another alternative embodiment of the field device of the invention provides that the control/evaluation unit configures, at least temporarily (for instance, after the opening or closing of a valve), parallel branches of function modules. The first branch is suited for processing abruptly changing process variables; the second branch is designed for processing essentially continuously changing process variables. Either the two branches work in parallel, or the branch suitable for the application is activated via the monitoring function.

The invention will now be explained in greater detail on the basis of the appended drawing, the figures of which show as follows:

FIG. 1 an embodiment of the partially dynamically configured, control/evaluation unit of the invention for a pressure measuring device; and

FIG. 2 a three-dimensional arrangement of a plurality of functionalities, with which different control/evaluating units for field devices can be configured.

FIG. 1 shows the control/evaluation unit 2 of a sensor 1, in this case, a pressure sensor, which is embodied in the form of a partially dynamically reconfigurable, logic chip FPGA 2 having a plurality of dynamically reconfigurable function modules 4. Two alternative methods for partially dynamically reconfiguring logic chips are described in two International patent applications, which have the same filing date as the present International patent application and which likewise claim the priorities of three patent applications filed on 17 Oct. 2006, namely: DE 10 2006 049 509.8, DE 10 2006 049 501.2, DE 10 2006 049 502.0. The content of these two International patent applications is expressly incorporated here by reference.

Provided on the control/evaluation unit 2 is at least one interface 25, via which the control/evaluation unit 2 receives sensor- and application-specific information concerning a defined sensor type—here, thus, the pressure sensor 1—in a defined process application—here, pressure measurement. Control/evaluation unit 2 configures the function modules 4 corresponding to the sensor- and application-specific information made available via the interface 25, so that the field device 3 is optimally adapted to the process variable p to be ascertained or monitored and to the current process application of the field device 3. The control/evaluation unit 2 receives the sensor- and application-specific information preferably during the manufacture of the field device 3. An option is, however, also, to reconfigure the field device 3 for another application at a later point in time. This reconfiguration can likewise be brought about via the operating, or servicing, tool 12. The function modules 4 are stored in the FLASH memory 18.

Via the physical interface 22, the sensor assembly 1, composed of a pressure sensor and a temperature sensor, detects the pressure p, in given cases, the pressure difference dp, and the temperature T. At the output of the sensor assembly 1, there is available a pressure measurement signal in the form of a resistance signal R=f(p, T)) or a capacitance signal C=f(p, T) and a temperature measurement signal in form of a resistance value R(T). As indicated by the functional dependence, the pressure measurement signal depends both on pressure and on temperature.

The resistance or capacitance values R, C are fed to A/D converter 6 and then filtered via the filter 7 a. On the basis of corresponding characteristic lines, in which case involved usually are polynomials, which are calculated in the unit 8, in the illustrated case the pressure p reigning in the process is ascertained.

As already earlier mentioned, pressure sensors are applied not only in the operational type, pressure measurement, but, also, in the operational types, flow measurement and fill level measurement. According to the invention, the control/evaluation unit I can be dynamically so configured, that the field device 3 is suitable, as a function of relevant application, alternatively for flow measurement or for fill level measurement. Corresponding function modules L, Φ can be dynamically partially configured.

The currently required function modules 4 are, on demand of the control program running in the microcontroller 23, partially dynamically configured in the logic chip FPGA. The configuring of the function modules 4 occurs in simple manner via a configuration bit stream, which is loaded from a memory FLASH 27. The configuring of the function modules 4 is described in detail in the two already earlier cited International patent applications, whose content is incorporated by reference in the present patent application.

Viewed as advantageous is to provide on the dynamically reconfigurable logic chip FPGA 2 two regions, a dynamic region DR and a static region SR. In the static region SR, in the illustrated case, the microcontroller 23 is permanently configured; therein runs the control program for configuration of the dynamic regions of the logic chip FPGA 2. Dynamic region DR is provided for the individual, dynamically configurable, function modules 4.

According to the invention, the function modules are always only partially configured, and, thus, resources used, which are currently required (see the first International patent application). By the therewith associated saving of area and resources, the control/evaluation unit 2 consumes only a fraction of the energy, which a usual FPGA requires. If this advantage is combined with the advantage of the solution based on permanently connected ASIC structures (see second International patent application), then the control/evaluation unit of the invention is distinguished additionally by the high processing speed of an ASIC.

The function modules 4 provide all needed functionalities, such as, for example, digital/analog conversion and the filtering of the measurement signal, the generating of an output value for the communication circuit, and the operating of the display/service unit.

A field device 3 having a partially dynamically reconfigurable logic chip FPGA 2 offers the advantage that only currently required function modules 4 are configured. All additional functionalities are, in principle, readily available, since they are stored as function modules 4 in a memory element 18 and can be configured at any time, to the extent that corresponding resources are available.

Through the partially dynamic configuration, relatively small FPGA chips with little memory capacity can be used. The smaller the logic chips, the less energy they require, while yet making functionality available to a high degree. Also, with the aid of the partially dynamic configuration, a very fast data processing is possible, since, for currently required functionalities, in principle, all resources of the dynamic region DR are available, whereby parallel execution is possible. Due to the small energy consumption, the field device 3 can be supplied with energy (loop powered) via a fieldbus 24, or a process control loop 10, without a separate energy supply line being necessary.

While, in FIG. 1, a concrete example of an embodiment of the field device 3 of the invention is described, the three-dimensional schema shown in FIG. 2 gives an indication of the enormous potential, which the solution of the invention opens for process automation technology. Through combination of the different variants and embodiments, any field device 3 for determining a process variable can be configured. Usually, such configuration occurs within the framework of the manufacturing process. The information is stored in the FLASH memory 18. Besides the configuring of the suitable control/evaluation unit 2 for the selected sensor type, the control/evaluation unit 2 can also, at any time, be adapted optimally to the particular application. Thus, the field device 3 can be equipped highly flexibly with the functionality of different device classifications. These are indicated in FIG. 2 with the labels of the planes, BASIC, STANDARD and ENHANCED.

The three-dimensional display shown in FIG. 2 will now be described in detail: In the rows of the front plane are presented a sensible sorting of different components of a field device 3. Of course, the illustrated functionalities represent only a selection. Given the multiplicity of possible variations, only a few are explicitly presented. The corresponding configurable function modules are stored in the field device 3.

Under the first. heading I/O—input/output—are some of the known inputs and outputs:

-   -   an in/output for a 4 . . . 20 mA measurement signal;     -   an in- and/or output unit in the form of a display 17 or a         keyboard;     -   a connection for digital data communication via fieldbus, e.g.         Profibus PA or Fieldbus Foundation FF;     -   a HART connection;     -   a connection to the Internet or to a firm-internal intranet.

In the second row are, by way of example, different process variables, which can be ascertained or monitored via the field device 3. Listed here explicitly are: Fill level, pressure, flow, temperature and analysis. Different options for the digital part on the front end are listed in the third row and referenced with capacitive, radiometry, absolute pressure, Coriolis and Time of Flight (ToF, or travel time).

Under the fourth row, ‘software stack’, different output values of the process variable are listed, such as distance, temperature, pH value or 4 . . . 20 mA. In the fifth row are provided test patterns, such as suitable in manufacture or for purposes of predictive maintenance or for SIL applications.

In the sixth row are provided adaptive function blocks, such as filter and algorithms.

In the depth direction, there are three planes, wherein the functionalities arranged in the first plane are associated with the lowest available ‘BASIC’ class of functionalities. The product classification of Endress+Hauser refers to this class of products as T class.

In the second plane are the functionalities, which correspond to the ‘STANDARD’ class of functionalities. Here, the classification of products applied by E+H refers to this as M class.

In the third plane are lastly the functionalities of the ‘ENHANCED’ class, which exceed the functionality of the M class and are associated with products of the so-called S class.

By way of example, the functionalities of a field device 3 of the lowest product-classification are selected—in FIG. 2, the selected function modules 4 are provided each with a circle. The partially configured field device 3 is a radiometric field device, which ascertains fill level of a fill substance in a container, and which outputs, as measured value, a 4-20 mA signal. Furthermore, an in/output unit is provided and the field device is able to communicate via the HART protocol.

LIST OF REFERENCE CHARACTERS

1 sensor

2 control/evaluation unit

3 field device

4 function module

5 microprocessor

6 A/D converter

7 signal filter

8 scaling of evaluating algorithms

9 modem

10 electrical current control unit

11 operating unit

12 operating, or servicing, tool

13 D/A converter

14 function block

15 analog interface

16 digital interface

17 display

18 memory unit: RAM/ROM/FLASH

19 EEPROM

20 UART

21 power fail RESET

22 physical interface

23 microcontroller

24 interface

25 interface

26 monitoring function 

1-11. (canceled)
 12. A field device for determining or monitoring a process variable in process automation, comprising: a sensor, which works according to a defined measuring principle; a control/evaluation unit, which conditions and evaluates measurement data delivered by said sensor; and interface, wherein: said control/evaluation unit is embodied at least partially as a reconfigurable logic chip FPGA having a plurality of dynamically reconfigurable function modules; said control/evaluation unit receives sensor- and application-specific information concerning a defined sensor type in a defined process application via said interface; and said control/evaluation unit so configures said function modules corresponding to the sensor- and application-specific information, that the field device is adapted optimally to the process variable to be determined, or to be monitored, and to the current process application of the field device.
 13. The field device as claimed in claim 12, wherein: the sensor- and application-specific information is provided to said control/evaluation unit in the context of production of the field device or in running, measurement operation.
 14. The field device as claimed in claim 12, wherein: said function modules include, for example, microprocessors with different bus rates, A/D converters or D/A converters with different bit resolutions, signal filters with different filter functions, different scalings of evaluating algorithms, different modems, different electrical current control units or operating units for different in/output units.
 15. The field device as claimed in claim 12, wherein: said control/evaluation unit has, besides the dynamic region, at least one static region, in which a fundamental component, such as, for example, a microcontroller, is permanently configured.
 16. The field device as claimed in claim 12, wherein: the sensor-specific information includes information, which characterizes said sensor via a defined measuring principle in its function for determining or monitoring a process variable.
 17. The field device as claimed in claim 12, wherein: the process variable comprises fill level, pressure, flow, temperature, conductivity, pH-value, turbidity, density, viscosity or concentration of a chemical substance.
 18. The field device as claimed in claim 12, wherein: the application-specific information comprises information concerning the defined application, in which the sensor (1) is applied in the process.
 19. The field device as claimed in claim 12, wherein: the application-specific information comprises information concerning in which operational type, e.g. pressure measurement, fill level measurement, flow measurement, said sensor, e.g. a pressure sensor, working according to a defined measuring principle, works.
 20. The field device as claimed in claim 12, wherein: the application-specific information comprises information on whether the field device is applied in a process with essentially constant values of the process variable or abruptly changing values of the process variable.
 21. The field device as claimed in claim 12, wherein: in ongoing measurement operation, a monitoring function checks, whether abrupt changes of the process variable occur; and said control/evaluation unit, in the case of abruptly changing values of the process variable, configures function modules, especially an ND converter, a D/A-converter and a signal filter, to have a lower resolution and a higher processing speed than in the case of slowly changing or constant values of the process variable.
 22. The field device as claimed in claim 12, wherein: said control/evaluation unit configures parallel branches of said function modules, which are suitable, on the one hand, for processing abruptly changing process variables, and which, on the other hand, are suitable for processing essentially continuously changing process variables, and that the monitoring function activates a suitable branch of function modules, depending on which case is present. 